Lance for blowing gases into contact with molten metal



LANCE FOR BLOWING GASES INTO CONTACT WITH MOLTEN META L Filed Dec. 29, 1966 R WURZBAHCH July 28, 1970 3 Sheets-Sheet 1 R. WU RZBACH July 28, 1970 v LANCE FOR BLOWING GASES INTO CONTACT WITH MOLTBN. METAL Filed Dec. 29, 1966 5 Siwets-Sheet 2 July 28, 1970 RwuRzBAcH I 3,521,871

LANCE FOR BLOWING GASES INTO CONTACT WITH MOLTEN METAL Filed Dec. 29, 1966 3 Sheets-Sheet 3 T N l i I l i i 14 0 I 3 Fig. 7

United States Patent Int. (:1. (the 7/04 US. Cl. 266-34 Claims ABSTRACT OF THE DISCLOSURE A lance particularly adapted for use with converters to direct a gas such as oxygen, in which solid particles may or may not be suspended, onto or into a molten metal, the lance having a discharge nozzle through which the gas issues. At the discharge nozzle the lance has an inner constriction reducing the area through which gas issues and spaced inwardly from an extremity of the discharge nozzle at the end of the lance where the discharge nozzle is located, the lance having in its interior a gasguiding means in the form of a body shiftable along the interior of the lance, spaced from the constriction, and formed at its exterior with helical grooves through which the gas flows to the nozzle so that the gas will spin substantially about the axis of the lance as it issues through the discharge nozzle, thus providing a substantially bellshaped stream of gas flowing from the discharge nozzle beyond the latter to the molten metal.

The development of lances for blowing oxygen or other gases, in which solid particles may, if necessary, be suspended, onto or into molten metal has been rendered diflicult because the actions which take place in the container for the molten metal and the manner in which the lance operates cannot be directly observed. Therefore, the more or less empirically developed different lance constrictions operate only partially in a satisfactory manner. In many cases conventional lances undergo rapid wear and breakdown as a result of the influences of high temperature and intended or unintended contact with the molten metal. Furthermore, in many cases the conventional lance structures cannot provide satisfactory operations.

It is accordingly a primary object of my invention to provide a lance which will avoid these and other drawbacks.

A particular object of my invention is to provide a lance which will produce a gas stream of predetermined configuration and moreover which will be capable of adjusting the configuration of the issuing gas stream.

It is especially an object of my invention to provide a lance which will produce a gas stream which issues from the lance with a substantially bell-shaped configuartion.

In contrast with the highly localized contact of a substantially conically shaped stream of gas with the surface of the molten metal, the bell-shaped stream of my invention, if situated at the same distance from the surface of the molten metal as a conventional substantially conical stream, will engage the surface of the molten metal not in a limited area hardly greater than a spot but rather over a much larger region of the surface of the molten metal across which the stream of gas is spread because of its bell-shaped configuration. Furthermore, a substantially conically shaped stream directs the gas along paths which are inclined at an angle other than a right angle with respect to the molten metal, whereas, in contrast, with the bell-shaped gas stream of my invention all of the "ice gas flows substantially perpendicularly to the surface of the molten metal when engaging the latter.

The lance structure of my invention makes use of a gas-guiding means which includes in the interior of the lance in the region of its discharge nozzle a body formed at its exterior with helical grooves which provide for the stream of gas a spinning action so that as a result the spinning gas stream has imparted to it a centrifugal force which immediately subsequent to movement of the stream beyond the lance provides a radial enlarging and spreading out of the gas stream and in addition achieves a rotary movement of the molten metal where the stream engages the latter.

The simple provision only of a spinning gas stream will not achieve the bell-shaped configuration for the stream. In accordance with my invention, this bell-shaped configuration is achieved by providing at the discharge nozzle of the lance an inner constriction which reduces the area through which the gas flows out of the discharge nozzle of the lance, and furthermore the gas-guiding means is situated within the lance at a given distance from the constriction. It has been found that the constriction of my invention influences the individual stream elements in such a way that the desired bell-shaped configuration is achieved.

The constriction of the lance of my invention takes the form of an inner annular bead situated directly at the outlet of the discharge nozzle. However, this construction creates the problem of protecting the bead from the influence of heat since the bead is located at that part of the lance where the thermal stress is at a maximum, so that the bead would be subjected to very rapid deterioration.

In order to avoid this latter problem, a further object of my invention includes providing a lance structure which will protect the bead from the high thermal stresses, and this latter object is achieved in accordance with my invention by displacing the bead inwardly from the extremity of the discharge nozzle which is situated at the discharge end of the lance so that the bead is situated inwardly from and spaced from the extremity of the discharge nozzle of the lance. This latter location of the head of my invention does not undesirably influence the manner in which the gaseous stream flows and in fact improves the flow characteristics since the discharge nozzle flares outwardly from the bead toward its extremity in a substantially conical manner.

It is of advantage to provide the gas-guiding body of the lance of my invention not only with exterior helicallyshaped grooves for the gas but also with a central axial bore which passes through the gas-guiding body so that one part of the stream of gas issues from the lance without having its direction of flow changed. Without in any way detracting from the desired flow characteristics achieved with the helically-shaped passages for the gas, there is produced with the axial bore of the gas-guiding body a reduction in the resistance to flow of the gas through the lance.

Depending upon the size of the converter and upon changing operating requirements, the gaseous stream will be distributed in a predetermined manner on the one hand for flow through the axial bore of the gas-guiding means and on the other hand for flow through the helical passages thereof. The adaptation to the operation requirements can of course be brought about by changing either the entire lance or the gas-guiding means thereof. However, in accordance with a further object of my invention, in order to simplify the adaptation of the lance to the above factors a construction is provided which is capable of directing a gas independently to the axial bore, as by providing a separate conduit means which communicates only with the axial bore of the gas-guiding 3 means, so that in this case through suitable throttling devices more or less gas can be directed through the axial bore.

Yet another object of my invention is to provide a construction which makes it possible to change the configuration of the bell-shaped gas stream issuing from the lance without dismantling or exchanging the lance and even during the operations during treatment of a charge. Thus, it has been found that the configuration of the bell-shaped stream, and in particular its diameter, is a function of the distance from that end face of the gas-guiding body which is directed toward the constriction and the latter constriction or bead, the bell-shaped stream spreading out to a greater extent the greater the distance between the gas-guiding means and the constriction. In order to make use of this discovery, the structure of my invention including a shifting means capable of axially shifting the gas-guiding means, particularly in a manner which renders this adjustment possible during treatment of a charge somewhat in such a way that initially the gas stream is directed in a concentrated manner on a sharply localized spot on the surface of the molten metal while during the further operations the concentration of the stream is reduced and the spreading thereof is increased. Moreover, the structure of my invention provides the possibility of carrying out adjustment of the stream during converter operations, adapting the operations to the different flow relationships which are required as a result of wearing away of the Wall of the converter resulting with the same amount of molten metal in different depths thereof.

Furthermore, it is an object of my invention to provide a construction which makes it possible to axially reciprocate the gas-guiding means in the lance so that during the blowing of a gas through the lance the gas guiding means will reciprocate therein thus providing a periodic concentration and widening of the area of contact between the stream and the molten metal. It has been found that treatment of the molten metal in this manner provides in many cases important metallurgical advantages.

It is a further object of my invention to provide a lance structure which solves the problem of cooling the lance. A lance having the above construction has particularly high cooling requirements as a result of the presence of the constriction at the discharge nozzle of the lance. In a conventional manner, the lance of my invention includes an elongated hollow tubular means having inner and outer tubular walls spaced from each other and including between these walls a tubular partition which defines an elongated tubular space with the inner wall and an elongated tubular space with the outer wall, this partition terminating in the region of the discharge nozzle in an end which is spaced from an annular end wall of the tubular means which interconnects the inner and outer walls thereof and which is situated at the extremity of the discharge nozzle. The cooling medium flows axially along the inner space between the tubular partition and inner wall toward the discharge nozzle where the cooling medium flows around the end of the tubular partition and then back along the outer tubular space which is between the tubular partition and the outer wall of the tubular means.

In order to achieve better cooling conditions, my invention includes an inner coating of chromium carried at the inner surface of the tubular means at the discharge nozzle thereof where the inner wall of the tubular means is contacted by the cooling medium. In this way the capability of resisting thermal loads is increased, since the chromium coating increases the extent to which the inner surface of the nozzle head can be contacted by liquids such as the molten metal.

Taking into consideration the fact that the thermal stressing of the lance increases with a reduction in the distance between the lance and the molten metal, the structure of my invention provides for the flow of the cooling medium in the interior of the tubular means a cross-sectional path of flow which continuously diminishes in the direction of flow of the cooling medium in the region of the discharge nozzle, so that the speed with which the cooling medium flows increases at this region and the cooling action is enhanced.

The lance is particularly stressed thermally in the immediately surrounding area of the discharge nozzle thereof. A simple reversal in the direction of flow of the stream of cooling water at this location changes the laminar flow characteristics of the cooling liquid into a disorderly type of flow with the further result that the turbulence created at this region provides in the cooling water portions which do not participate in the continuous flow thereof through the interior of the lance and instead provide portions of the cooling medium which linger and remain in the region of the discharge nozzle to finally vaporize in the interior of the tubular means. In order to avoid this latter drawback, a further feature of my invention provides at the place where the direction of flow of the cooling medium is reversed a continuous reduction in the cross section of the area of flow.

Lances of the above type are not only thermally stressed to a great extent at their discharge nozzles as a result of the high temperature in the space immediately surrounding the discharge nozzle, but also they are highly stressed at this region because they are subjected to spattering and splashing of the molten metal. As a result the lance is subjected to mechanical stresses, especially if in addition to the oxygen or other gas solid particles are blown with the gas onto the molten metal. In many cases even a properly cooled lance is not equal to these thermal and mechanical stresses.

It is accordingly also an object of my invention to provide a construction which will overcome the latter problem. This result is achieved, in accordance with my invention, by providing for the head of the lance, where the discharge nozzle thereof is located, at the exterior surface of the lance which defines the inner and outer surrounding surfaces of the discharge nozzle thereof a coating which is particularly resistant to the conditions prevailing during converter operations, such as to heat and/ or corrosion. For this purpose the coating is made of metals of high melting point such as tungsten, tantalum, molybdenum, chromium or similar metals, as well as oxides of metals of high melting point. Zirconium oxide has proved to be particularly effective. By constructing the discharge nozzle head of the lance in this manner there is provided the possibility of immersing the discharge nozzle directly in the molten metal.

Of course, the extent of protection provided by a layer of this latter type increases with its thickness. However, thick layers of this type are inclined to peel away from and become separated from the surfaces on which they are initially located. It is therefore yet another object of my invention to avoid this latter problem, and the solution to this latter problem is achieved according to my invention by dividing the protective coating into a plurality of individual layers.

In order to take full advantage of the properties of the metal of high melting point on the one hand and the oxide thereof, on the other hand, as well as to render the tendency of the metal to corrosion to become ineffective, one of the features of my invention resides in providing at least two layers, namely an inner layer consisting of a metal of high melting point and an outer layer consisting of an oxide of a metal of high melting point,

My invention is illustrated by way of example in the accompanying drawings, which form part of this application and in which:

FIG. 1 is a fragmentary schematic, partly sectional side elevation of the entire assembly;

FIG. 2 is a longitudinal sectional elevation of one possible embodiment of a lance according to my invention at the region of the discharge nozzle thereof;

FIG. 3 is a sectional plan view of the structure of FIG.

2 taken along line IIIIII of FIG. 2 in the direction of the arrows;

FIGS. 4 and 5 respectively illustrate different positions of the gas-guiding means with the different stream configurations resulting from these different positions;

FIG. 6 is a simplified schematic illustration of the structure of FIG. 1 as seen in the direction of the direction of the arrow VI of FIG. 1;

FIG. 7 shows the parts of FIG. 6 in a different position;

FIG. 8 shows on a smaller scale than FIG. 2 a fragmentary longitudinal section of another embodiment of a lance of my invention in the region of the discharge nozzle thereof; and

FIG. 9 is a fragmentary sectional elevation, at a highly enlarged scale, of the outer Wall structure of the discharge nozzle.

The structure which is illustrated in FIG. 1 corresponds in general to the conventional structure. The tubular means 1 of the lance of my invention is fixed at its outer wall to an arm 2 which is rigidly fixed with the frame 3. In order to feed the oxygen or other gas, the structure includes a turnable arm 4 which carries a flexible tube or hose 5. The arms 4 are supported for turning movement on a shaft 7 which is carried by a suitable supporting beam 6.

The hose 5 is not directly connected to the tubular means 1, but instead has a flange connection with an inner tube 8 which is longitudinally shiftable within the tubular means 1. In order to prevent escape of gas from the top end of the tubular means 1, a seal is provided, and this seal can have the form of a stuffing box and appears in FIG. 1 in the form of a pair of flanges 9.

As is apparent particularly from FIGS. 6 and 7, the inner tube 8 can be vertically displaced by a pair of hydraulic cylinder-and-piston drives carriedby the frame 3 and including the cylinders 10 which coact with the pistons 11. The pistons 11, in the manner shown in FIGS. 6 and 7, have pivotal connections 14 with the ends of a pair of cross members 12 which are in turn provided with pivotal connection 13 to the inner tube 8.

For cooling purposes the lance has a conventional double-walled construction. Thus, the outer tubular wall of the tubular means 1 surrounds and is spaced from an inner tubular wall 15, and a tubular partition 16 is situated between the inner and outer tubular walls of the tubular means 1, so as to form a pair of elongated tubular spaces 17 and 18 which are connected to each other by an annular end wall of the tubular means situated at the extremity 19 of the discharge nozzle and interconnecting the inner and outer tubular walls, the partition 16 terminating in an end which is spaced from the annular end wall at the extremity 19 so as to provide around the end partition 16 a space where the direction of flow of the cooling liquid can be reversed, this cooling liquid, such as water, for example, flowing downwardly through the space 17 and upwardly the space 18, as shown by the arrows in FIG. 2. For the reasons which have been set forth above, the inner surface of the inner tubular wall is provided at the discharge nozzle of the lance with a coating of chromium which is not illustrated. The cooling liquid which flows down the space 17 and up the space 18 is cooled by the oxygen which flows through the interior of the lance, and in this way the cooling liquid in the space 17 is maintained at a low temperature.

The longitudinally shiftable inner tube 8 serves to carry a gas-guiding means formed by a body 20 which is of substantially cylindrical configuration and which fills, with suitable tolerances, together with the wall of the inner tube 8, the transverse space which is surrounded by the inner wall 15 of the tubular means. This body 20 of the gas-guiding means is formed with a central axial bore 21 passing therethrough as Well as with a number of outer helically-shaped grooves which together with the inner surface of the inner tube 8 define the helical passages 22. The oxygen which is supplied to the lance passes through the gas-guiding means 20 along a pair of different paths, namely without having its direction changed while flowing through the central bore 21 and on the other hand with a change in direction as a result of flowing through the helicallyshaped passages 22. The stream which is achieved by way of the flow of the oxygen through the helical grooves 22 thus spins around the axis of the lance.

At the region of the lance extremity 19, but somewhat displaced therefrom, the discharge nozzle is provided with an inner constriction in the form of a bead 23, and this bead is of particular significance for achieving the desired configuration of the stream of gas which issues from the lance.

Without entering into a discussion of relatively complex flow conditions, experience which has been provided by testing has shown that the gas stream which issues from the nozzle of FIG. 2 has the configuration of a bell, as indicated in FIGS. 4 and 5. The bell-shaped gas stream will be spread out to a greater extent, the greater the distance of the gas-guiding means 20 from the extremity 19, as may be seen from a comparison of FIG. 5 with FIG. 4. Thus, if the gas-guiding means 20 is displaced from the position of FIG. 5 to the position of FIG. 4, the spreading of the gas stream will be reduced and a more concentrated stream will be achieved, as is apparent from FIG. 4. The metallurgical ladvantages of the bell-shaped stream and the advantages to be achieved by adjusting the breadth of this stream have already been discussed above.

The drive means 10, 11 shown in FIGS. 6 and 7 makes it possible not only to change the axial position of the gas-guiding means 20 at every instant during treatment of one charge or during changeover from one charge to another, but in addition it makes it possible to give to the gas-guiding means a reciprocating motion back and forth during the blowing operations, and in fact with an amplitude and frequency which can be changed within wide limits. Experience up to the present time has shown that movement with reciprocation at a frequency range of approximately 1 Hz. is particularly suitable in order to provide the metallurgical process with a favorable influence.

The helically-shaped passages 22 together with the bead 23 result in the formation of the bell-shaped stream which issues from the lance. On the other hand, it is not essential to provide the axial bore 21 for this purpose. The best results are achieved with the variation shown in FIG. 8 where the central axial bore 21 and the helical passages 22 are separately provided with gas. For this purpose an additional conduit 24 is connected to and communicates with the central axial bore 21, extending down to the latter, through the inner tube 8 from the top toward the bottom thereof, so that it becomes possible through separate feed conduits and throttling or shut-off devices to selectively supply only the helical passages 22 with gas or in addition the central bore 21 in any quantitatively selected manner.

The construction shown in FIG. 2 takes particular care of the problem of cooling. The inner elongated tubular space 17 has a relatively large cross section so that the cooling medium will flow axially through the space 17 at a relatively slow rate, and thus can be effectively cooled with the low-temperature oxygen which flows through the discharge nozzle. As the space 17 approaches the extremity 19, it is provided in the region 25 '-with a cross section which becomes continuously smaller in the direction of flow, so that the speed of flow increases and the cooling action is intensified. However, there is still the danger that at the reversal in the direction of flow from the passage 17 to the passage 18 there will be turbulence in the cooling liquid with the resulting formation of steam bubbles which great- 1y reduce the extent of cooling. The construction shown in FIG. 2 solves this latter problem by providing between the end of the inner tubular partition 16 and the annular end wall at the extremity 19 which defines the flow-reversing space a a cross section of flow which continues to diminish in the direction of flow, so that the cross sectional area of the path through which the fluid flows becomes continuously smaller even during reversal in the direction of flow, and thus the predetermined laminar flow of the cooling medium is maintained even during reversal in the direction of flow.

As has already been pointed out above, the head 23 is displaced inwardly from the extremity 19 of the discharge nozzle. This construction is suitable also from the standpoint of cooling. A bead situated directly at the extremity 19 would be exposed to a maximum extent to the heat of the molten metal, and thus deprived to a large extent of the influence of the cooling medium. These disadvantages are avoided by the illustrated location of the head 23 according to the invention. Moreover, the outward flaring of the nozzle between the head 23 and the extremity 19 where the nozzle has the inner substantially frustoconical surface 26 contributes favorably to the desired formation of the issuing gas stream.

For the reasons which have been set forth above, the discharge nozzle is provided at its outlet and at the area surrounding its outlet with a protective coating. This protective coating is illustrated generally at 27 in FIG. 2 and extends from the upper edge 28 of the bead 23 down to the extremity 19 and upwardly along the outer surface of the outer wall of the tubular means to the location 29.

The construction of the coating 27 is shown at a highly enlarged scale in section in FIG. 9. This coating consists in the illustrated example of seven individual layers which are situated on the tubular wall 30 which is made of copper, for example. The innermost layer 31 of nickelchromium alloy is followed by a thin layer 32 of molybdenum, and on the latter layer there is a layer 33 of zirconium oxide. The layer is surrounded and engaged by a further layer 34 of molybdenum which forms the carrier for a second layer 35 of zirconium oxide. Between the latter layer of zirconium oxide and the outer layer 36 which also consists of zirconium oxide, there is a third layer 37 of molybdenum. The outermost zirconium oxide layer 36 is substantially thicker than the remaining two layers of this material. a

I claim:

1. A lance particularly adapted for use with converters for directing a gas into contact with molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gasguiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said construction an end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shiftin the latter back and forth within said tubular means during operation thereof.

2. The combination of claim 1 and wherein said tubu lar means has an end face at an extremity of said discharge nozzle thereof and said constriction being in the form of an annular bead displaced inwardly from and thus spaced from said extremity of said nozzle.

3. A lance for directing a gas into contact With a molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means andincluding a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction and end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth within said tubular means, said tubular. means having an end face at an extremity of said discharge nozzle thereof and said constriction being in theform of an annular bead displaced inwardly from and. thus spaced from said extremity of said nozzle, said discharge nozzle flaring outwardly from said bead to said extremity; thereof and having a substantially frustoconical configuration between said bead and extremity. 1

4. A lance for directing a gas into contact with a molten metal, comprising elongated tubular means terminating at one end inadischarge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gasflows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction an end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth within said tubular means,'said body of said gas-guiding means being formed with an axial bore passing therethrough.

5. The combination of claim 4 and wherein a conduit means communicates with said axial bore of said body for directing a fluid therethrough independently of other fluid which flows through said tubular means.

I 6. The combination of claim 1 and wherein the stroke of said gas-guiding means is adjustable.

'7. A .lance for directing a gas into contact with a molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction an end face which is spaced therefrom said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth within said tubular means, said tubular means including an outer tubular wall, an inner tubular wall spaced from and surroundedby said outer tubular Wall, and an end wall situated at said discharge nozzle and interconnecting said inner and outer tubular walls of said tubular means, the latter further including a tubular partition situated between said inner and outer walls and terminating short of said end wall so that a cooling fluid may flow between said tubular partition and inner'wall toward said dis charge nozzle and around an end of said tubular partition at said end wall between the latter and said end of said tubular partition and back between said tubular 8. The combination of claim 7 and wherein the space defined between said end of said tubular partition and said end wall continues the continuous decrease in the cross section of flow of a cooling fluid around said end of said end wall from said elongated annular space.

9. A lance for directing a gas into contact with a molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction an end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth within said tubular means, said tubular means including an outer tubular wall, an inner tubular wall spaced from and surrounded by said outer tubular wall, and an annular end wall interconnecting said inner and outer tubular walls and situated at said discharge nozzle, said tubular means further including an inner tubular partition spaced from and situated between said inner and outer tubular walls to define therewith an inner elongated tubular passage situated between said partition and inner tubular wall and an outer elongated tubular passage situated between said outer tubular wall and said tubular partition, said tubular partition terminating in the region of said discharge nozzle in an end spaced from said end wall to define with the latter an annular space where the direction of flow of a cooling fluid flowing along said inner space to said outer space changes, said space defined between said end wall and end of said partition having a constantly diminishing cross sectional area in the direction of flow of a cooling fluid from said inner to said outer space.

10. A lance for directing a gas into contact with a molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction an end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth within said tubular means, said tubular means including an elongated hollow tubular member provided at its inner surface with a coating of chromium.

11. The combination of claim 1 and wherein said tubular means has in the region of said nozzle an outer coating which is resistant to conditions encountered in a converter.

12. The combination of claim 11 and wherein said coating is made of a metal having a high melting point.

13. The combination of claim 12 and wherein said metal is selected from the group consisting of tungsten, tantalum, molybdenum, and chromium.

14. The combination of claim 11 and wherein said coating includes an oxide of a metal of high melting point.

15. A lance for directing a gas into contact with a molten metal, comprising elongated tubular means terminating at one end in a discharge nozzle and having at said discharge nozzle an inner constriction reducing the area of the discharge nozzle through which a gas may issue, elongated gas-guiding means situated in said tubular means and including a body formed at its exterior with helical grooves through which a gas flows toward said discharge nozzle, said gas-guiding means guiding gas toward said discharge nozzle to issue therethrough and having directed toward said constriction an end face which is spaced therefrom, said gas-guiding means being axially shiftable within said tubular means, and shifting means operatively connected with said gas-guiding means for axially shifting the latter back and forth Within said tubular means, said tubular means having in the region of said nozzle an outer coating which is resistant to conditions encountered in a converter, said coating including at least two layers one of which is an inner layer consisting of metal of high melting point and the other of which is an outer layer consisting of an oxide of a metal of high melting point.

References Cited UNITED STATES PATENTS 1,146,394 7/1915 Best 239-488 X 2,829,960 4/1958 Vogt 26634.1 X 3,045,997 7/ 1962 Hudson 266-34.1 3,241,825 3/1966 Jilek et a1. 26634.1 3,292,662 12/ 1966 Nishi 26634.1 3,321,139 5/1967 De Saint Martin 239-1323 3,379,428 4/ 1968 Dortenzo et al 26634.1

FOREIGN PATENTS 81,700 11/1915 Austria. 808,111 1/1937 France.

I. SPENCER OVERHOLSER, Primary Examiner US. Cl. X.R. 239-1323 

